1. Field of the Invention
The present invention relates to a coated cemented carbide endmill exhibiting excellent wear resistance for a long period of time.
2. Description of the Background
Conventionally, coated cemented carbide endmills are composed of a tungsten carbide (WC) based cemented carbide substrate (hereinafter "cemented carbide substrate") having a surface portion with an average layer thickness of 0.5-5 .mu.m of hard-material-coated-layers composed of a Ti compound. The Ti compound is one or more layers of a titanium carbide (TiC), titanium nitride (TiN), titanium carbide-nitride (TiCN), titanium oxy-carbide (TiCO), titanium oxy-nitride (TiNO) and titanium oxy-carbo-nitride (TiCNO). Each of the hard-material-coated-layers is formed by medium temperature chemical vapor deposition (MT-CVD) (a method in which vapor deposition is performed at 700-980.degree. C., a temperature lower than the vapor deposition temperature 1000-1150.degree. C. employed by ordinary high temperature chemical vapor deposition (HT-CVD)), as shown in, for example, in Japanese Unexamined Patent Publication No. 62-88509.
In order to save labor and energy, there has been a tendency to increase cutting speed in a cutting process. When the conventional coated cemented carbide endmills are used under these high speed conditions, the hard-material-coated layers tend to exfoliate due to insufficient adhesion, resulting in endmills which are remarkably worn and which have a relatively short life.